The IceCube Neutrino Observatory's measurement of a diffuse flux of neutrinos from astrophysical sources has opened a new era in high energy astroparticle physics. Neutrinos produced by cosmic ray interactions in the atmosphere are the main background to the astrophysical neutrino flux. At these high energies, data from the Large Hadron Collider experiments can be used to narrow the uncertainties in the background predictions. After reviewing the properties of neutrinos, the atmospheric neutrino flux will be used to illustrate one way that collider physics results are connected to cosmic ray physics.